Radio frequency (RF)-excited waveguide (and non-waveguide) lasers have found a large number of applications in the past several years because of their compact size, reliability, and ease of manufacture. The basic RF-excited waveguide laser was disclosed in U.S. Pat. No. 4,169,251 by Katherine D. Laakmann. Many other patents exist that cover various other laser structures having plasma tube discharge sections that are electrically excited by radio frequency voltages between a pair of electrodes. All of these lasers have in common a resonating or traveling wave discharge structure using inductors to neutralize the capacitive reactance of the discharge electrodes.
The drive impedance created by this matching technique is essentially real (ohmic), in order to realize an impedance match to an independent source of RF energy. These excitation sources are generally crystal-controlled amplifier chains operating on one of the FCC-authorized ISM frequencies at 13, 27 and 40 MHz. With extreme shielding, operation on non-ISM frequencies between 30 and 200 MHz is also feasible and practiced by some companies.
This known method of independent laser excitation (or pumping) has been worked out quite well and it has been quite satisfactory for prior art devices. However, with the disclosure by Peter Laakmann of an all metal gas laser structure in a pending U.S. patent application Ser. No. 857,354, now abandoned, these amplifier chains become a very significant or even the dominant part of the total laser cost. It is therefore desirable to excite the plasma tube of a gas laser by means of oscillator circuitry that can cause the laser to be electrically self-oscillating and can require fewer components.
An additional problem with the prior art is that the laser shows two impedance levels that have to be matched to the amplifier: the high-impedance operating state prior to breakdown of the plasma and the low-impedance state after breakdown. This means that the amplifier must be a compromise that will provide operation in both modes.
It is also therefore desirable to have an RF-excited gas laser that incorporates an oscillator circuit that automatically adjusts to the changeable parameters of the lasing gas medium.